Extracting metals from their ores is an energy intensive process. After extraction, the metals are commonly alloyed in different proportions to achieve certain physical or chemical characteristics. When the useful life of objects using these metals and alloys is over, they are typically sent to scrap yards and shredded to smaller pieces to be sold as aggregated scrap metals. Value of such aggregates is much lower compared to the fresh alloys, since they cannot be simply re-melted and re-used, due to their unknown composition. While lab methods such as atomic emission spectroscopy can identify each sample, the time taken for testing each sample may be several minutes, and requires sophisticated and expensive analytical tools. Therefore the cost of identification far outstrips the residual value of the scrap metal itself.
A large industry segment in the scrap materials business makes and uses machines that broadly separate some of the scrap components very fast, in matter of seconds. For instance, air-vortex separators remove plastics; Eddy-current separators remove glasses and plastics; Magnetic separators remove ferrous items; and X-ray assisted conveyor belts remove high atomic weight metals such as copper. However, within the same metal families, identifying and separating different alloys at a fast speed of seconds or less has been a challenge.
Several hand-held and portable instruments and technologies exist today that are capable of identifying different alloys, but they have not been integrated to high throughput conveyor-belt systems due to their slower speeds of 30 seconds to several minutes per test. Such technologies include: (a) X-ray fluorescence spectroscopy and (b) Laser-ablation spectroscopy, and variations and combinations of these. In X-ray spectroscopy, an X-ray beam excites the orbital electrons of the surface of the scrap sample, resulting in optical fluorescence. The fluorescence spectrum is measured by sensitive photo-detectors. Each metal has a characteristic spectrum, and by de-convoluting the spectrum, the metal components in the alloy can be determined. In Laser-ablation method, a very high power laser beam vaporizes a small amount of the surface of the sample, and an optical emission or absorption spectroscopy is done on the vapor to determine its composition. Both these technologies require 10-40 seconds to measure each sample, and cost between US$ 20,000 and US$ 40,000, making it prohibitive for implementation in conveyor-belt sorters. For such sorters, the identification must be made within a few seconds.